R2A (Reasoner’s 2A) agar is used for water testing because it is a low-nutrient
medium that supports the growth of a wide variety of heterotrophic bacteria. The
primary reasons for using R2A agar in water.
Water samples often contain microorganisms that are stressed or slow-growing due to
low nutrient levels. R2A agar provides a suitable environment for these organisms to
recover and grow.
R2A agar is formulated to support the growth of diverse microbial populations,
including those that might be missed by nutrient-rich media. This makes it ideal for
comprehensive water quality testing.
R2A agar is typically incubated for longer periods (up to 5 days), allowing for the
detection of slow-growing bacteria that are significant in water systems but might not
be detected with shorter incubation times.
Many regulatory guidelines and standard methods for water quality testing, such as
those from the U.S. Environmental Protection Agency (EPA) and Standard Methods
for the Examination of Water and Wastewater, recommend the use of R2A agar for
heterotrophic plate counts.
Water flora will be in stressed condition, if we provide high nutrient media it can not
survive. R2A is low in nutrients that to simple nutrients which are easy to digest.